A jack-up is a mobile well-drilling marine unit, which can float and be towed to a designated drilling station, where the legs are lowered to rest the feet on the bed of the body of water, or drive the feet in, when working on soft beds. The floating structure is then raised above the surface of the water, to above maximum wave and/or tide level; and, once the jack-up is supported firmly on the bed of the body of water, drilling of the bed is commenced.
A drilling program comprises drilling a plurality of wells in designated locations spread over a designated area. The operating range of the jack-up depends on its structural characteristics. More specifically, the maximum length of its legs depends on how the jack-up is constructed, and the maximum water depth jack-ups can operate in rarely exceeds a hundred meters, whereas the minimum drilling depth is normally about six meters, and depends on the jack-up's tonnage and draught.
Drilling programs sometimes call for drilling with a jack-up in very shallow water, (i.e., shallower than the minimum allowed by the jack-up's tonnage and draught); in which case, other types of jack-ups must be used, thus greatly increasing overhead of the drilling program as a whole.